"Our health and safety representatives who look out for workers' health and safety are not reporting a problem."

Dr Napthine described building sites as potentially dangerous environments.

"We want people operating major machinery in dangerous environments to be drug- and alcohol-free, just the same as we demand pilots to be drug- and alcohol-free, drivers of trucks and heavy vehicles to be drug- and alcohol-free," he told Fairfax Radio.

"The Masters Builders Association have been lobbying for this, it's been comments from the police expressing concern about drugs through outlaw motorcycle gangs being dealt on building sites, but most of all it's been driven by a need for occupational health and safety."

CFMEU occupational health and safety manager Dr Gerry Ayers said there is no evidence of drug dealing on the sites.

"If the police have information about bikies selling drugs on sites then they should investigate and act on illegal activity," he said.

The plan will also force companies bidding for government projects to install CCTV monitoring, biometric scanning and smartcard technology on their sites.

Opposition Leader Daniel Andrews said construction workers could be asking why the laws will apply to them and not the premier.

He said he would support an alcohol-free parliament.

Planning Minister Matthew Guy says he hopes the CFMEU will support mandatory drug testing on building sites.

"We believe it's something that should be welcomed by the CFMEU and other unions because we're trying to make workplaces safer for workers on building sites across Victoria," he told reporters.

He said similar tests were already in force on many private building sites.